I wouldn't call my thighs or hips a "problem" but they definitely are bigger, proportionally, than, say, my arms (I have matchstick arms - really).

However, they have changed in the last two years of cycling. They did tone up and I obviously have lost inches down there because now I can pull down my jeans (which fit a bit tightly in the legs area when I bought them exactly a year ago, at the end of my first intense summer of cycling) without undoing the button and zipper. This happened without me losing a single pound on the scale. This is probably not very surprising considering that I have cycled 5000 km in between, but I find it annoyingly expensive to have to buy a few new pairs of pants again.

I haven't done any special exercises besides pedalling, save for 8 sessions of core-training that did have quite an impact on my core, but not really on my thighs.

So the bottom line is: it takes time and mileage.